1. Field of the Invention
The present invention relates to a vibration wave device such as an ultrasonic wave motor, which utilizes the resonance of a vibrator.
2. Related Background Art
Recently, a vibration wave motor called an ultrasonic wave motor or a piezoelectric motor has been developed and put into practical applications by the present applicant. As is well known, the vibration wave motor is a new type of non-electromagnetic driven motor, in which an alternative voltage is applied to an electro-mechanical energy conversion element such as a piezoelectric element or an electro-strictive element to cause it to generate a high-frequency vibration, and the vibration energy is picked up as a continuous mechanical motion. Since the principle of the operation of this motor has already been described in many laid-open patent applications such as Japanese Laid-Open Patent Application No. 3-289375 by the present invention, a detailed description thereof will be omitted.
FIG. 15 is a side view of a conventional rod-shaped ultrasonic wave motor and a diagram showing the voltage to be applied to piezoelectric elements constituting the motor and output voltages therefrom. A vibrator 1 constitutes the rod-shaped ultrasonic wave (vibration wave) motor, and comprises a coupled body of piezoelectric elements or electro-strictive elements and elastic members.
The piezoelectric element portion of the vibrator portion 1 comprises A-phase driving piezoelectric elements a1 and a2, B-phase driving piezoelectric elements b1 and b2, and a vibration detection piezoelectric element s1. When an A-phase application voltage is applied to a portion sandwiched between the A-phase piezoelectric elements a1 and a2 via an electrode plate A-d, and a B-phase application voltage is applied to a portion sandwiched between the B-phase piezoelectric elements b1 and b2 via an electrode plate B-d, these piezoelectric elements are driven.
The surfaces, opposite to the corresponding electrode plates, of the A- and B-phase piezoelectric elements a1, a2, b1, and b2 are set at the GND potential via electrode plates GND. One surface (the B side of s1 in FIG. 15) of the vibration detection piezoelectric element s1 is similarly set at the GND potential, and a signal is picked up from the other surface via an electrode plate S-d. The signal pickup surface side of the vibration detection piezoelectric element s1 contacts a metal block, which is insulated from the GND potential using an insulating sheet. Therefore, an output voltage corresponding to a vibration can be directly obtained from the vibration detection piezoelectric element s1. Then, a resonance frequency or the like is calculated on the basis of the magnitude of the output voltage, the phase differences from the driving voltages, and the like.
FIG. 16 shows a driving circuit using the above-mentioned ultrasonic wave motor. This circuit includes an oscillator 2 for generating an alternative voltage, a 90.degree. phase shifter 3, switching circuits 4 and 5 for switching a power supply voltage using the alternative voltages from the oscillator and the phase shifter, and booster inductance elements 6 and 7 and capacitance elements 8 and 9 for amplifying the pulse voltages switched by the switching circuits 4 and 5. The boost amounts change depending on the values of these inductance and capacitance elements. More specifically, the input electric power characteristics to the motor can be changed depending on the values of these inductance and capacitance elements. The circuit also includes a phase difference detector for detecting the signal phase difference between a driving electrode A and a vibration detection electrode s1. A control microcomputer 11 sets the driving frequency, and the ultrasonic wave motor is driven at the set frequency.
However, the conventional arrangement of the driving circuit for the ultrasonic wave motor requires electric elements such as the switching circuits, the booster inductance elements, the capacitance elements, and the like in addition to the ultrasonic wave motor, resulting in high parts cost. In addition, in products such as still cameras, video cameras, and the like which require size reductions, it is difficult to mount the above-mentioned circuit on a circuit board.
In particular, the conventional ultrasonic wave motor shown in FIG. 15 can realize an ultra size reduction (e.g., its diameter is equal to or smaller than that of a pencil), and hence, the size of the driving circuit to be mounted on a board such as a flexible printed board is preferably reduced as much as possible.